This invention relates to the electrostatically-aided atomization and coating of articles. It is disclosed in the context of a facility in which articles to be coated electrostatically are conveyed past coating equipment on a conveyor, but is believed to be useful in other applications as well.
In a typical coating system, articles to be coated are generally transported through a coating zone on a mechanical conveyor. The conveyor is typically maintained at or near ground potential and the articles to be coated are supported on the conveyor by hangers which are intended to maintain the parts as nearly as possible at the potential of the conveyor. A coating dispensing device includes some means for charging the dispensed particles of coating material to high-magnitude potential, typically high-magnitude negative potential, with respect to the potential of the conveyor.
Intermittent contact or high-impedance contact between the articles to be coated and the conveyor can result in less than ideal coating results, and waste of coating material. This occurs because the charged coating material, which should migrate along electric field lines from the dispensing device, which is maintained at high-magnitude potential, to the low-magnitude potential maintained on the articles to be coated, instead migrates along field lines established between the dispensing device and other articles and surfaces in the vicinity of the dispensing device which are maintained at low-magnitude potential, such as the conveyor itself. The charged particles of coating material which should be coating the articles are not.
The coating material is thus wasted. And, not only is the coating material wasted, but the wasted coating material particles are deposited on, and coat, components of the conveyor and the hangers upon which the articles to be coated are suspended from the conveyor. This can result in components of the conveyor and hangers being partly coated with the coating material, and buildup of coating material on components of the conveyor and hangers over time. Thus, the pathways to ground for charge on the dispensed coating material sometimes become more and more resistive with time, and less and less of the charged coating material is attracted to, and deposited on, the articles which are to be coated by the coating material. This, in turn, requires removal of components of the conveyor and hangers to be removed from service and cleaned after passing through the coating zone, so that after a number of successive passages, they will not be so covered with a layer of coating material which is sufficiently insulating to prevent electrical contact between the articles to be coated and the grounded conveyor. In summary, many of the benefits associated with electrostatically aided atomization and coating are lost if the articles to be coated are not properly grounded to terminate the electrostatic field.
The need for hangers and associated types of devices for suspending articles to be coated from conveyors for conveying past coating dispensing equipment is well established. Several types of such equipment are known. There are, for example, the devices illustrated and described in U.S. Pat. Nos. 3,777,875; 3,787,707; 3,844,477; 3,873,024; 3,981,471; 4,097,359; 4,217,853; 4,628,859; 4,703,716; 5,147,050; 5,476,689; 5,524,774; 5,551,552; 5,598,099; 5,757,606; 5,776,554; 5,824,403; 5,908,120; 5,949,235; and, 6,325,899, PCT published applications: WO 96/26406; WO 97/00730; and, WO 01/68265, and European published applications 0 308 142 and 1 034 846. There are also the disclosures of U.S. Pat. Nos. 4,508,768; 4,853,128; 4,902,547; 5,020,761; 5,328,137; 5,542,634; 5,728,440; 5,832,859; and, 5,890,604. No representation is intended by this listing that this is a complete listing of all pertinent prior art, or that a thorough search of all pertinent prior art has been conducted, or that no better prior art exists. Nor should any such representation be inferred.
According to one aspect of the invention, hangers are provided for coupling articles to a conveyor for conveyance through electrostatically charged coating material. The hangers are constructed from electrically non-insulative strips.
According to another aspect of the invention, an apparatus for coating articles with coating material includes means for dispensing coating material, means for maintaining the coating dispensing means at high-magnitude electrostatic potential, means for coupling articles to a conveying means. The coupling means includes hangers constructed from electrically non-insulative strips. The means conveys the articles through the dispensed coating material on the hangers.
According to another aspect of the invention, an apparatus for coating articles with coating material includes a coating dispensing device for dispensing coating material, a conveyor for conveying articles past the coating dispensing device to be coated by coating material dispensed from the coating dispensing device, a high-magnitude potential supply for maintaining the coating dispensing device at high-magnitude electrostatic potential, and hangers for coupling articles to the conveyor. The hangers are constructed from electrically non-insulative strips.
Illustratively according to these aspects of the invention, the electrically non-insulative strips are flexible.
Further illustratively according to these aspects of the invention, the electrically non-insulative strips include strips of foil or tape treated to render them electrically non-insulative.
Additionally illustratively according to these aspects of the invention, the electrically non-insulative strips are treated on two sides to render two sides electrically non-insulative.
Illustratively according to these aspects of the invention, each strip includes two opposite ends, and further including an electrically non-insulative adhesive on one side adjacent the two ends.
Further illustratively according to these aspects of the invention, the adhesive permits attachment of a strip to two sides of a respective article, creating a loop for suspending the respective article from the conveyor.
Additionally illustratively according to these aspects of the invention, the strips of foil or tape treated to render them electrically non-insulative include strips of foil or tape metallized to render them electrically non-insulative.
According to another aspect of the invention, a method for coating articles with coating material includes dispensing coating material from a coating dispensing device, maintaining the coating dispensing device at high-magnitude electrostatic potential, coupling articles to a conveyor on hangers constructed from electrically non-insulative strips, and conveying the articles through the dispensed coating material on the hangers.
Illustratively according to this aspect of the invention, coupling articles to the conveyor on hangers constructed from electrically non-insulative strips includes coupling articles to the conveyor on hangers constructed from flexible, electrically non-insulative strips.
Further illustratively according to this aspect of the invention, coupling articles to the conveyor on hangers constructed from electrically non-insulative strips includes coupling articles to the conveyor on hangers constructed from strips of foil or tape treated to render them electrically non-insulative.
Additionally illustratively according to this aspect of the invention, coupling articles to the conveyor on hangers constructed from strips of foil or tape treated to render them electrically non-insulative includes coupling articles to the conveyor on hangers constructed from strips of foil or tape treated on two sides to render two sides electrically non-insulative.
Illustratively according to this aspect of the invention, coupling articles to the conveyor on hangers constructed from strips of foil or tape treated to render them electrically non-insulative includes coupling articles to the conveyor on hangers constructed from strips of foil or tape including two opposite ends, and further including providing an electrically non-insulative adhesive on one side adjacent the two ends.
Further illustratively according to this aspect of the invention, the method includes attaching a strip using the adhesive to two sides of a respective article, thereby creating a loop for suspending the respective article from the conveyor.
Additionally illustratively according to this aspect of the invention, treating the strips of foil or tape to render them electrically non-insulative includes metallizing the strips of foil or tape to render them electrically non-insulative.
According to another aspect of the invention, a coated article is made by dispensing coating material from a coating dispensing device, maintaining the coating dispensing device at high-magnitude electrostatic potential, coupling the article to a conveyor on a hanger constructed from an electrically non-insulative strip, and conveying the article through the dispensed coating material on the hanger.
Illustratively according to this aspect of the invention, the coated article is made by coupling the article to the conveyor on a hanger constructed from a strip of foil or tape treated including two opposite ends, and provided with an electrically non-insulative adhesive on one side adjacent the two ends.